Epoxy resins have good workability, and form cured products that are excellent in the electrical properties, thermal resistance, adhesiveness, moisture resistance (water resistance) and the like. The epoxy resins are used in a wide range of applications such as electric/electronic elements, structural materials, adhesives and coating materials.
However, in recent years, along with the development in the electric and electronic fields, there is a demand for further improvements in the general properties of a resin composition, such as purity enhancement, improvements in moisture resistance, adhesiveness and dielectric properties, viscosity lowering intended for filling in more fillers, and reactivity enhancement intended for making molding cycles shorter. Also, as for a structural material, there is a demand for a material having light weight and excellent mechanical properties, in the applications of aerospace materials, instruments for leisure and sports activities, and the like. Moreover, in recent years, although halogen-based epoxy resins and antimony trioxide are largely used as flame retardants, and particularly as flame retardants for electric and electronic elements, products using these materials have been accused of contributing to the generation of toxic materials such as dioxin, due to inappropriate waste treatment thereof. As an exemplary method for addressing the problems described above, Patent Document 1, Patent Document 2 or the like describes the use of a phenol aralkyl resin having a biphenyl skeleton, or an epoxide of such resin. However, resins having this structure have a strong tendency to crystallize, and thus crystals precipitate out depending upon the conditions for isolating the resin during the production, or the storage conditions, thus resulting in an increase in the melt viscosity. Furthermore, even in the case of dissolving the resin in a solvent, crystals precipitate out and settle down, and causing a serious problem in the use as a composition.
Under such circumstances, it has been investigated in Patent Document 3 to lower this crystallizability by controlling the orientation properties, but the results are still unsatisfactory.    Patent Document 1: Japanese Patent Application Laid-open No. 11-140277    Patent Document 2: Japanese Patent Application Laid-open No. 11-140166    Patent Document 3: Japanese Patent Application Laid-open No. 2003-301031